Low-profile antennas are commonly used in vehicles. The antennas are typically mounted on an exterior of the vehicle. For aesthetic reasons, the antennas are preferably small in size. The vehicle may have several antennas in one antenna assembly or network.
Several conventional low-profile antennas include multiple parts. Since large volumes are produced, reducing the number of parts used to manufacture the antenna can significantly reduce the cost. For terrestrial applications, the antenna should maximize transmit/receive signals in lateral directions while minimizing signals in a vertical direction.
U.S. Pat. No. 5,652,595 to Ahrens et al. describes a patch antenna having reactive loading. The patch antenna includes several different layers and materials, which are costly to manufacture. U.S. Pat. No. 5,784,032 to Johnston et al. describes a planar antenna having several shorting tabs. However, the planar antenna does not allow high capacitive loading. Increased capacitive loading allows the antenna to be made with a lower profile for a given frequency of operation. U.S. Pat. No. 6,014,105 to Davis et al. describes a microstrip antenna that includes multiple parts and has a relatively high manufacturing cost. The microstrip antenna feed is located off-center, which reduces efficiency for terrestrial reception. An article by M. Deshpandea and Y. Rao, “Analysis of Reactively Loaded Microstrip Disk Antenna”, in IEEE Proceedings, Vol. 136, No. 5, describes a patch type antenna having a tab extending from a body of the patch. However, the tab produces circular polarization and is not used for impedance matching. A traditional feed is still needed for the patch antenna.
A common way of making these antennas involves using two metal pieces. A first metal piece forms a top plate. A second metal piece provides shorting pins. The metal pins are typically bent out of the plate to reveal slots. Ordinarily, the slots would form part of the antenna design, to make the antenna smaller or more broad-band, or the slots would be designed out. When the first and second metal pieces are soldered together, the slots are typically eliminated.